1. Field of the Invention
The present invention relates to a shift control apparatus for an automatic transmission having an automatic shift mode and a manual shift mode.
2. Description of the Related Art
Shift control in an automatic transmission for a vehicle is usually performed according to a shift characteristic map for setting gear positions according to vehicle running conditions. In this shift control, each vehicle running condition according to which gear shift is performed is uniquely defined, so that flexibility in gear shift is low and it is difficult for an operator to determine when a shift operation has been performed during running. In this respect, there has recently been commercially available a vehicle mounting an automatic transmission having a manual shift mode where a shift operation can be performed also by a manual operation by the operator.
Generally in such an automatic transmission, a manual range is additionally set at a shift position of a shift lever to be operated by the operator, and every time an upshift command or a downshift command is output by the operation of the shift lever in the manual range, the present gear position in the automatic transmission is sequentially shifted to higher gear positions or lower gear positions.
Further, there has been proposed in Japanese Patent Laid-Open No. 2000-283281 or 2002-147588 an automatic transmission having a manual shift mode where upshift or downshift is allowed according to operator's desire by depressing a switch provided on a steering wheel during running in a drive range (D range) of the automatic transmission.
Further, Japanese Patent Laid-open No. 2003-139238 discloses shift hold control such that when a predetermined operational condition (kick-down) is detected, an upshift line is displaced toward higher vehicle speeds, and when the vehicle running condition becomes a condition where an upshift signal is to be output beyond the upshift line, the output of the upshift signal is delayed by a predetermined time period.
Thus, the automatic transmission described in Japanese Patent Laid-Open No. 2000-283281 or 2002-147588 includes a shift control apparatus allowing upshift or downshift by a switch operation during running in the D range, so that the operator can enjoy driving in the manual shift mode according to operator's desire. However, in this prior art shift control apparatus for the automatic transmission, fine control in shifting from the automatic shift mode to the manual shift mode has not been disclosed. Accordingly, the operator cannot enough enjoy manual-like driving faithful to operator's desire in the manual shift mode.
In the shift control apparatus for the automatic transmission described in Japanese Patent Laid-Open No. 2002-147588, the condition for return from the manual shift mode to the automatic shift mode is composed of three conditions that the lateral acceleration (lateral G) is less than or equal to a predetermined value, that the vehicle is not during inertial running, and that the vehicle speed is greater than or equal to a predetermined speed. However, these conditions for return to the automatic shift mode are susceptible to consideration from the viewpoint of smooth mode shifting.